These views of Callisto were taken in May 2001 by the Galileo spacecraft. The top insert shows the sharp, knobby terrain experiencing erosion. As they stand now, the knobs are about 80 to 100 meters (260 to 330 feet) tall. As these knobs erode and disappear, the terrain will look more and more like the bottom insert. The smallest features discernable in these images are about 3 meters (10 feet) across. Courtesy of NASA/JPL/Arizona State University